The present invention relates to a radar system for detecting an object by transmitting an electromagnetic wave comprising a laser beam or a millimeter wave toward the object and receiving a reflected wave thereof.
There are conventionally known laser radar systems mounted in a vehicle for detecting the position of a preceding vehicle traveling ahead of the vehicle and the distance between the vehicle and the preceding vehicle, which systems are shown in FIG. 10.
In the system shown in FIG. 10A, a laser beam emitted by a laser diode LD is reflected by a first mirror M1 which is reciprocally turnable about a rotational axis S, and scans laterally as a transmitted-beam elongated vertically with its lateral width thereof limited. A beam receiving area elongated vertically with a limited lateral width is scanned laterally by a second mirror M2 which is reciprocally turnable integrally with the first mirror M1, and the wave reflected from an object is caught in the beam receiving area and received by a photo-diode PD.
In the system shown in FIG. 10B, a laser beam emitted from the laser diode LD is reflected by a mirror M reciprocally turnable about a rotational axis S, and scans laterally as a transmitted-beam elongated vertically with its lateral width limited. The wave reflected from an object is caught in a fixed beam receiving area and received by a photo-diode PD.
In the system shown in FIG. 10C, a laser beam emitted from a laser diode LD is reflected by a polyhedral mirror HM rotatable about a rotational axis S, and scans laterally and vertically as a transmitted-beam with lateral and vertical widths limited. The wave reflected from an object is caught in a fixed beam receiving area and received by a photo-diode PD.
Meanwhile, in the prior art systems shown in FIGS. 10A to 10C, the vertically elongated beam receiving area and the fixed beam receiving area are used. For this reason, as shown in FIG. 11, in some cases, the sun rays may enter the beam receiving area at such times of the day as in the morning or evening when the sun is low. As a result, there is the possibility that the amount of received-beam could be saturated due to the direct sun rays, thereby making it impossible to detect a preceding vehicle. If the vertical width of the beam receiving area is set at a small value in order to avoid this, there is the possibility that the preceding vehicle may go out of the beam receiving area, because of the aiming of the beam transmitted to the preceding vehicle being slightly displaced vertically, or because of the pitch angle of the vehicle being slightly varied due to the influence of a load carried on the vehicle, or due to the influence of the inclination of a road surface, thereby making it impossible to detect the preceding vehicle.
The present invention has been accomplished with the above circumstances in view, and it is an object of the present invention to provide a radar system, wherein the influence of the direct sun rays can be maintained to the minimum thereby to detect an object reliably, without need for a precise aiming.
To achieve the above object, according to the present invention, there is provided a radar system characterized by comprising an electromagnetic wave transmitting means for transmitting an electromagnetic wave, a first scanning means for laterally scanning with the electromagnetic wave transmitted from the electromagnetic wave transmitting means as a transmitted-beam elongated vertically with a lateral width thereof limited, a second scanning means for vertically scanning a receiving area elongated laterally with a vertical width thereof limited to catch the electromagnetic wave reflected from an object, and a reflected-wave receiving means for receiving the reflected wave caught in the receiving area.
With the above arrangement, the electromagnetic wave transmitted from the electromagnetic wave transmitting means scans laterally as a transmitted-beam elongated vertically with its lateral width limited by the first scanning means. The wave of the transmitted-beam reflected from the object is caught in the receiving area which is elongated laterally with the vertical width limited and scanned vertically by the second scanning means, and is received by the reflected-wave receiving means.
Even if the vertical width of the transmitted-beam is set at a sufficiently large value in order to absorb an error in the vertical mounting of the radar system to reliably detect the object, the object can be detected reliably, excluding the case where the height position of the sun corresponds to the level of the object, if the period of time when the direct sun rays enter the receiving area to make the detection impossible is shortened by vertically scanning the laterally elongated receiving area. Thus, the influence of the direct sun rays can be maintained to the minimum even at such times of the day as in the morning or evening when the sun is low, thereby enhancing the ability to detect the object.
In addition, according to the present invention, there is provided a radar system characterized by comprising an electromagnetic wave transmitting means for transmitting an electromagnetic wave, a first scanning means for vertically and laterally scanning with the electromagnetic wave transmitted from the electromagnetic wave transmitting means as a transmitted-beam having limited lateral and vertical widths thereof, a second scanning means for vertically scanning a receiving area elongated laterally with a vertical width thereof limited to catch the electromagnetic wave reflected from an object, and a reflected-wave receiving means for receiving the reflected wave caught in the receiving area, wherein a period of scanning by the second scanning means is equal to a period of vertical scanning by the first scanning means.
With the above arrangement, the electromagnetic wave transmitted from the electromagnetic wave transmitting means scans vertically and laterally as a transmitted-beam having the limited lateral and vertical widths by the first scanning means, and the wave of the transmitted-beam reflected from the object is caught in the receiving area which is elongated laterally with the vertical width limited and scanned vertically by the second scanning means, and is received by the reflected-wave receiving means. At this time, a period of vertical scanning by the second scanning means is equal to a period of vertical scanning by the first scanning means.
Even if the vertical width of vertical scanning of the transmitted-beam is set at a sufficiently large value in order to absorb the error in the vertical mounting of the radar system to reliably detect the object, the object can be detected reliably, excluding the case where the height position of the sun corresponds to the level of the object, if the period of time when the direct sun rays enter the receiving area to make the detection impossible is shortened by vertically scanning the laterally elongated receiving area. Thus, the influence of the direct sun rays can be maintained to the minimum even at such times of the day as in the morning or evening when the sun is low, thereby enhancing the ability to detect the object. Moreover, because the beam density can be increased by limiting the transmitted-beam in the vertical and lateral widths, even if the output of the electromagnetic wave transmitting means is decreased, a required beam density can be provided, and also the weather resistance such as at the time of rain or snow can be enhanced by increasing the beam density with the output of the electromagnetic wave transmitting means maintained intact.